The present invention is generally related to wheeled vehicles. More particularly, the present invention is directed to a wheel suspension systems for wheelchairs.
Motorized mid and rear-wheel drive wheelchairs typically include a front wheel assembly that is designed to engage the ground either continuously or sporadically, such as during climbing. In the embodiment where the front wheels are continuously on the ground, the wheel and suspension assembly are configured to carry some of the vehicle and occupant weight during operation. These types of wheels may have a caster configuration where the wheel is free to turn as needed to account for the movement of the vehicle.
In the second embodiment where the front wheels are only sporadically in contact with the ground, the front suspension holds the wheels in an elevated position with respect to the ground. The wheels are, again, typically caster type wheels.
In both types of conventional front suspension systems for wheelchairs, the suspension system is subjected to loading and displacements along or about a lateral axis (i.e., an axis extending from side-to-side of the wheelchair) and a fore-aft axis caused by one or both of the wheels contacting an object in path of travel. FIG. 1 illustrates a front wheel of a conventional wheelchair contacting an object on the ground. The object forces the wheel to move up and over the object. In many wheelchairs, the wheels are fixedly attached to the chair frame. As such, the contact with the object results in the chair being raised upward and tilted to the side. Not only is this unnerving for the user, but the impact, lifting and dropping of the chair is also uncomfortable. Also, as the vehicle transitions over rough ground, fixedly attached wheels transmit vibratory and oscillatory loads to the chair and, hence, the user. While the use of resilient tires provides some reduction in the transmission of loads (such as vibration and oscillation loads) they generally can not provide the necessary compliance to sufficiently absorb the shocks generated on rough terrain and/or upon hitting small obstacles. These unabsorbed shocks and oscillations are transmitted to the rider and result in an uncomfortable ride.
In order to minimize the displacements and loads produced by the wheel hitting an object, some conventional front wheel assemblies incorporate a resilient suspension system. These systems permit limited deflection of the front wheel with respect to the front wheel support. These suspension systems also help absorb the force of the contact that occurs when the wheel hits the object. One such system is shown in U.S. Pat. No. 6,234,507. In the embodiment shown in FIG. 8 of the ""507 patent, two resilient rubber members are located within a support housing this is mounted to the frame. The resilient members surround a shaft located on each individual wheel assembly. Upon hitting an object the shaft portion is permitted to twist slightly with respect to the housing, thus accommodating some displacement of the wheel about a lateral axis.
While the suspension system in the ""507 patent accommodates some of the loads and displacements described above, it does not sufficiently accommodate displacements and loading about the longitudinal (fore-aft) axis. Furthermore, the entire front suspension (wheels and frames) must be deflected before the resilient rubber elements can accommodate any of the loading or displacements.
A need, therefore, exists for an improved front wheel suspension system for a wheel chair.
The present invention relates to a suspension system for mounting a pair of wheels to a main frame of a wheelchair. In one preferred embodiment, the suspension system includes a crossbar pivotally mounted to the wheelchair so as to pivot about an axis that is parallel to the longitudinal axis of the wheelchair.
At least one spring element is located between and mounted to the crossbar and the wheelchair frame for controlling the pivoting of the crossbar. The spring biases the crossbar against rotation while also minimizing the transmission of vibratory loads. Preferably there are two spring members, one located on either side of the pivotal mounting point of the crossbar.
A hinge assembly is mounted on each lateral end of the crossbar. The hinge assembly includes a first hinge component attached to the crossbar so as to be rotatable about a vertical axis. A second hinge component is resiliently connected to the first hinge component. The resilient connection biases the second hinge connection against rotation with respect to the first hinge component and minimizes the transmission of vibratory and oscillatory loads.
A wheel and yoke assembly are mounted to the second hinge component. The hinge assembly allows the wheel and yoke to deflect upon contact with an obstacle in the wheelchairs path.
Other objects, aspects and advantages of the present invention will become apparent to those skilled in the art upon reading the following detailed description, when considered in conjunction with the appended claims and the accompanying drawings briefly described below.